U.S. patent number 4,482,277 [Application Number 06/468,368] was granted by the patent office on 1984-11-13 for expansion anchor assembly.
This patent grant is currently assigned to Hilti Aktiengesellschaft. Invention is credited to Erwin Schiefer.
United States Patent |
4,482,277 |
Schiefer |
November 13, 1984 |
Expansion anchor assembly
Abstract
An expansion anchor assembly is made up of an anchor bolt and an
expansion sleeve encircling and secured in an annular recess on the
bolt. Adjacent the annular recess, the anchor bolt has a
frusto-conical section. The expansion sleeve has diametrically
opposite reduced thickness wall sections with a projection
extending outwardly of the surface of the sleeve along each of the
reduced thickness wall sections. When the expansion anchor assembly
is inserted into a prepared borehole and the frusto-conical section
is drawn into the sleeve, the sleeve breaks into axially extending
sections along the reduced thickness wall sections and a uniform
contact is provided between the sleeve section and the borehole
surface.
Inventors: |
Schiefer; Erwin (Munich,
DE) |
Assignee: |
Hilti Aktiengesellschaft
(Schaan, LI)
|
Family
ID: |
6156366 |
Appl.
No.: |
06/468,368 |
Filed: |
February 22, 1983 |
Foreign Application Priority Data
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Feb 22, 1982 [DE] |
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3206290 |
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Current U.S.
Class: |
411/42; 411/39;
411/63 |
Current CPC
Class: |
F16B
13/065 (20130101) |
Current International
Class: |
F16B
13/06 (20060101); F16B 013/04 () |
Field of
Search: |
;411/60,39,42,73,71,64,63,68 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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953546 |
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Aug 1974 |
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CA |
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1318704 |
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Jan 1963 |
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FR |
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556980 |
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Dec 1974 |
|
CH |
|
12749 |
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Oct 1914 |
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GB |
|
905941 |
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Sep 1962 |
|
GB |
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1211245 |
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Nov 1970 |
|
GB |
|
Primary Examiner: Holko; Thomas J.
Assistant Examiner: Lindsey; Rodney M.
Attorney, Agent or Firm: Toren, McGeady and Stanger
Claims
I claim:
1. An expansion anchor assembly comprising an axially extending
anchor bolt and an axially extending expansion sleeve, said anchor
bolt having a first end and a second end, said anchor bolt has a
cylindrically shaped outside surface for an axial portion thereof
extending from the first end, and a frusto-conicaly shaped outside
surface extending from adjacent the second end toward the first end
with said frusto-conically shaped surface tapering inwardly toward
the first end, a cylindrically shaped annular recess in said anchor
bolt extending from the smaller diameter end of said
frusto-conically shaped surface toward the first end, said recess
has a smaller diameter than the cylindrically shaped outside
surface extending from the first end, said expansion sleeve is a
hollow cylinder and is positioned in said annular recess and
encircles said anchor bolt, said expanion sleeve has an inside
surface and an outside surface and said expansion sleeve has an
axially and circumferentially extending region in the inside
surface thereof recessed outwardly from the surface of said annular
recess forming a reduced thickness wall section acting as a
predetermined breaking location for said expansion sleeve, wherein
the improvement comprises that said inside surface of said
expansion sleeve is cylindrically shaped and fits closely around
said cylindrically shaped annular recess in said anchor bolt, in
the circumferentially extending region of said reduced thickness
wall section a projection is formed extending radially outwardly
from the cylindrically shaped outside surface of said expansion
sleeve.
2. An expansion anchor assembly, as set forth in claim 1, wherein
said projection extends in the axial direction of said sleeve along
said reduced thickness wall section.
3. An expansion anchor assembly, as set forth in claim 2, wherein
two diametrically oposite reduced thickness wall sections are
provided in said expansion sleeve with one said projection
associated with each of said reduced thickness wall sections.
4. An expansion anchor assembly, as set forth in claim 2, wherein
said projection is in the form of a web having a smaller dimension
in the circumferential direction of said expansion sleeve than said
reduced thickness wall setion.
5. An expansion anchor assembly, as set forth in claim 3, wherein
said reduced thickness wall sections divide said expansion sleeve
into two half sections, and a hinge provided in each said half
section spaced between said reduced thickness wall sections, and
said hinges each form a swivel axis extending parallel to the axis
of said expansion sleeve.
6. An expansion anchor assembly, as set forth in claim 2, wherein
said reduced thickness wall sections are formed by axially
extending grooves provided in the inside surface of said expansion
sleeve.
7. An expansion anchor assembly, as set forth in claim 6, wherein
said grooves are substantially rectangular in cross-section
extending transversely of the axial direction of said expansion
sleeve.
8. An expansion anchor assembly, as set forth in claim 7, wherein
one generally radially extending side of said groove is longer than
the other radially extending side of said groove so that the
reduced thickness wall section remaining varies in thickness across
the circumferential direction of said groove in said expansion
sleeve.
9. An expansion anchor assembly, as set forth in claim 2, wherein
said projection has a dimension in the circumferential direction of
said expansion sleeve substantially equal to the comparable
dimension of said reduced thickness wall section.
10. An expansion anchor assembly, as set forth in claim 2, wherein
said projection has a saw-tooth like configuration.
11. An expansion anchor assembly, as set forth in claim 10, wherein
said projection is secured to said sleeve at the opposite axial
ends thereof and is separated from said sleeve between said ends.
Description
SUMMARY OF THE INVENTION
The present invention is directed to an expansion anchor assembly
made up of an essentially cylindrically shaped anchor bolt and an
expansion sleeve encircling and secured in an annular recess in the
anchor bolt. The anchor bolt has an axially extending
frusto-conical section extending from the annular recess and
widening in the direction away from the recess. The expansion
sleeve is a hollow cylinder and has reduced thickness sections
which form predetermined breaking regions. The reduced thickness
sections are formed in the side surface of the expansion sleeve so
that the inside surface of the reduced thickness section is spaed
radially outwardly from the surface of the annular recess in the
anchor bolt.
Expansion anchor assemblies of this type are used in large numbers,
because of their economical construction and the ease with which
they can be set. These anchor assemblies are used in a great many
different fields. High strength concrete is usually the receiving
material into which the anchor assemblies are set.
In this type of expansion anchor assembly, the expansion sleeve
which encloses the anchor bolt in an annular recess formed in the
bolt, is radialy expanded to achieve the anchoring effect.
Accordingly, the expansion sleeve has a slot which extends over its
full axial length. To achieve as uniform as possible a radial
widening, the expansion sleeve is also provided with a reduced
thickness or weakened section opposite the slot, and this reduced
thickness section forms a predetermined breaking line when the
sleeve is expanded.
The setting procedure is effected by inserting the expansion anchor
assembly so that the expansion sleeve is located within a
cylindrical bore in a receiving material. When the anchor bolt is
subsequently retracted or pulled out of the bore, such as by means
of a nut screwed onto a threaded end section of the anchor bolt
projecting out of the bore, the frusto-conical section of the bolt
moves into the expansion sleeve which is temporarily held in the
bore, such as by a prestressing action. The expansion sleeve
experiences radially directed stress and breaks along the reduced
thickness or weakened section. If breakage occurs, the separated,
half-shell shaped sections are pressed against the wall of the bore
by the frusto-conical section of the anchor bolt as the anchor bolt
is retracted or pulled out of the bore.
Based on experience, it has been noted that the predetermined
breaking locations do not respond reliably in the known expansion
anchor assemblies. In some instances, the expansion sleeve remains
intact when the frusto-conical section of the bolt moves into the
sleeve. The surface of the expansion sleeve has uneven contact as
it continues to expand, that is, it is deflected toward the surface
of the bore primarily in the region between the slot and the
reduced thickness section. An uneven distribution of the anchoring
pressure results.
In hard receiving materials, such as conentional concrete, only
relatively low anchoring values can be attained, since there is
only a partial application of force relative to the capacity of the
receiving material. Due to this pressure distribution
characteristic, and also when the expansion anchor assembly is used
in low strength receiving materials as compared to conventional
concrete, only low anchoring values are achieved relative to the
specified force capacity of the expansion anchor assembly. The
uneven pressure distribution leads to locally excessive stresses on
the receiving material so that the receiving material tends to
spall causing the anchor to be displaced out of the bore.
Therefore, it is the primary object of the present invention to
provide an expansion anchor assembly which is easy to set in place
and is distinguished by a uniform application of force against the
surface of the bore into which it is placed so that high anchoring
values can be achieved in receiving materials of different
strength.
In accordane with the present invention, in the region of the
reduced thickness or weakened cross-section, a projection is
provided extending outwardly from the cylindrical outer surface of
the expansion sleeve.
Preferably, one or more cam-like shaped projections are provided
extending along the weakened cross-sectional regions of the sleeve
at its outer cylindrical surface. When the expansion anchor
assembly is inserted into a bore, the projections contact the bore
surface. Subsequently, when the frusto-conical section of the bolt
is drawn into the expansion sleeve, of necessity, the projections
press radially inwardly against the reduced thickness or weakened
cross-sectional areas providing a reliable breakage of the sleeve.
The axially extending sleeve sections formed in this manner are
pressed uniformly against the surface of the bore during the
continuous expansion of the sleeve. As a result, a uniform
application force over the entire circumference of the expanding
sleeve takes place within the bore.
When this expansion anchor assembly is used in conventionally hard
concrete, a comparatively higher anchoring value can be achieved
due to the pressure distribution over a large surface. In lower
strength receiving materials, the uniform pressure distribution
permits a higher expanding force which creates comparatively high
anchoring values.
When the cross-sectional weakening or reduced thickness sections
extend over the entire or major part of the axial length of the
expansion sleeve, then it is preferable if the projection also
extends along the length of the weakened section. Where a
projection extends continuously over the full length of the
cross-sectionally weakened section, it increase the certainty that
the sleeve breaks along its entire length at the predetermined
breaking location. After the sleeve breaks along the weakened
section, the weakened section along with the projection move
radially inwardly into the resulting slot-like open space between
the sleeve sections. Accordingly, the projection does not impair
the anchoring of the sleeve surface to the surface of the bore.
The expansion sleeve is securely held on the anchor bolt when the
sleeve does not have a longitudinal slot. Further, it is
advantageous if the expansion sleeve has two diametrically opposite
cross-sectional weakened or reduced thickness sections with a
projection extending along each section. Such an arrangement
assures the formation of two axially extending sleeve sections due
to the breakage along the weakened sections, so that a completely
uniform pressure distribution takes place along the cylindrical
surface of the expansion sleeve.
The projection may extend radially outwardly from the sleeve across
the width of the weakened or reduced diameter section, that is, it
extends for the full circumferential dimension of the section. It
is advantageous to form the cross-sectionally weakened sections by
forming dies. The edge transition between the reduced thickness or
recessed zones formed in such an operation relative to the adjacent
undeformed section affords a breaking region.
In one embodiment of the invention, the projection is constructed
as a web with a smaller circumferential width than that of the
cross-sectionally weakened section. Such an arrangement facilitates
breakage of the weakened section. The weakened section, in
addition, is advantageously formed so that its thickness varies in
the circumferential direction of the expansion sleeve. In this
manner, the separation along the predetermined breaking region can
be controlled as desired in connection with the formation and
arrangement of the reduced thickness section.
In another embodiment of the invention, the expansion sleeve is
divided into sections by means of axially extending highes formed
in the expansion sleeve and spaced between two adjacent
projections. As a result, the hinges have a swivel axis extending
parallel to the sleeve axis. When the sleeve ruptures along the
predetermined breaking regions as the anchor assembly is being set,
the sections formed in the breaking operation are deformable to a
large extent due to the hinges so that practically an ideal,
uniformly circular contact of the outside surface of the expansion
sleeve and the surface of the bore is attained.
The hinges can be produced by providing sleeve parts which hook
into one another. By providing a snap connection between the hinge
parts, even after the separation takes place along the
predetermined breaking regions, a secure hinge engagement is
maintained, and this hinge construction permits a simple assembly
of the expanding sleeve during the manufacture of the expansion
anchor assembly.
The various features of novelty which characterize the invention
are pointed out with particularity in the claims annexed to and
forming a part of this disclosure. For a better understanding of
the invention, its operating advantages and specific objects
attatined by its use, reference should be had to the accompanying
drawings and descriptive matter in which there are illustrated and
described preferred embodiments of the invention .
BRIEF DESCRIPTION OF THE DRAWING
In the drawings:
FIG. 1 is an axially extending side view of an expansion anchor
assembly embodying the present invention with the assembly ready to
be inserted;
FIG. 2 is an enlarged cross-sectional view through the expansion
anchor assembly taken along II--II in FIG. 1;
FIG. 2a is a sectional view similar to that shown in FIG. 2 taken
along the line II--II of FIG. 1, however, the expansion anchor
assembly has been set in place;
FIG. 3 is a detail of a partial cross-section of an expansion
anchor assembly, similar to that in FIG. 2, with a different
construction of the expansion sleeve;
FIG. 4 is a partial sectional view similar to FIG. 3, showing an
expansion anchor assembly like the one in FIG. 2, but with a
different construction of the expansion sleeve;
FIG. 5 is a partial sectional view similar to the expansion anchor
assembly in FIG. 2, however, with a different construction of the
expansion sleeve; and
FIG. 6 is a side view of the expansion sleeve shown in FIG. 5 taken
in the direction of the arrow VI in FIG. 5.
DETAIL DESCRIPTION OF THE INVENTION
In FIG. 1 an expansion anchor assembly is illustrated made up of an
axially elongated anchor bolt 1 and an expansion sleeve 2 mounted
on the bolt. The main axially extending portion of the anchor bolt
is cylindrically shaped and it has a circular recess 3 adjacent to
the frusto-conically shaped section 4 adjacent the leading end of
the bolt. As viewed in FIG. 1, the right-hand end of the bolt is
its leading end, that is the end which is inserted first into a
borehole. The frusto-conical section 4 tapers outwardly toward the
leading end of the bolt. The cylindrically shaped section of the
bolt extending from the recess 3 to the trailing end is provided
with a thread 5 running from the trailing end. A nut, not shown,
can be screwed onto the thread 5.
As shown in FIG. 2, expansion sleeve 2 is made up of two sleeve
half sections 6, 7 secured together at diametrically opposite
location by reduced thickness sections 8, 9 which provides weakened
sections extending along the sleeve. The reduced thickness section
8, 9 are in the form of recesses or grooves 11, 12 extending
outwardly from the inside surface of the sleeve and the grooves
have a generally rectangular cross-section extending in the axial
direction of the sleeve . The reduced thickness sections 8, 9
formed by the groove 11, 12 define predetermined breaking regions
extending along the axial direction of the sleeve. The depth of the
grooves 11, 12 increases in one circumferential direction so that
the wall of the sleeve 2 has a residual thickness a at one side of
the groove smaller than residual thickness b at the other side of
the groove. As shown in the lower portion of FIG. 2, the thickness
a extends along the groove half section 6 while the other thickness
b extends along the sleeve half section 7. On the outside surface
of the sleeve half sections 6 and 7, in the area of the reduced
thickness sections 8, 9, projections in the form of axially
extending, rib-shaped webs 13, 14 are provided. Each sleeve half
section 6, 7 is divided in the axial direction equidistantly spaced
from the reduced thickness sections by means of hinges 15, 16.
Accordingly, each sleeve half section is made up of two parts
secured together by the hinges 15, 16. The hinges are formed by
projections 15a, 15b, 16a, 16b which interlock with one
another.
To set the expansion anchor assembly, it is inserted into a
previously prepared bore 17, note FIG. 2a, in a receiving material
18 and the diameter of the bore is not sigificantly larger than the
diameter of the anchor bolt. The webs 13, 14 on the expansion
sleeve 2 project slightly outwardly beyond the outside surface of
the sleeve and, as can be seen in FIG. 1, also beyond the outside
surface of the section of the anchor bolt extending to the trailing
end. The outside surface of the sleeve 2 has approximately the same
diameter as the adjacent axially extending cylindrically shaped
surface of the anchor bolt 1. As the expansion anchor assembly is
inserted into the bore 17, the webs 13, 14 dig into the surface of
the bore and provide a preliminary or temporary holding action
within the receiving material 18.
To facilitate the insertion of the expansion sleeve 2 into the
opening into the bore 17, the leading ends 19 of the webs are
beveled.
With the anchor bolt 1 of the expansion anchor assembly inserted
into the bore a sufficient distance so that the sleeve 3 is located
interiorly of the opening into the bore, the nut is run onto the
thread 5 until it bears against the surface of the receiving
material 18. As the nut is tightened onto the thread 5 while it
contacts the surface of the receiving material 18, the
frusto-conical section 4 is drawn in the direction out of the bore
so that it moves into the expansion sleeve 2 which is held within
the bore by the webs 13, 14. As the frusto-conical section 4 moves
into the sleeve, the sleeve begins to expand radially outwardly.
The radially projecting webs 13, 14 forced against the surface of
the bore 17 provide increasing compressive stress on the
predetermined breaking regions formed by the reduced thickness
sections 8, 9 until the smaller residual thickness a is unable to
withstand the stress after a small amount of expansion has taken
place, with the result that the sleeve ruptures along the edges of
the grooves 11, 12 defined by the smaller thickness a. The rupture
of the reduced thickness sections 8, 9 is shown in FIG. 2a. When
the rupture takes place, the web 13, 14 and the wall portions of
the expansion sleeve outwardly of the grooves 11, 12 deflect
inwardly into the space left by the grooves, note FIG. 2a.
As the anchor bolt 1 continues to move rearwardly into the sleeve 2
the breaking apart of the sleeve half sections 6, 7, continues and
the outside surfaces of the sleeve half sections are displaced
radially outwardly against the surface of the bore 17 in the
receiving material 18. The hinge 15, 16 permit the hinged parts of
the sleeve half sections 6, 7 to swivel outwardly and adapt their
diameter to the diameter of the anchor bolt which widens as the
frusto-conical section continues to move rearwardly within the bore
through the sleeve. As a consequence, the outside surface of the
sleeve half sections rest for their full circular extent against
the inside surface of the bore 17 and thus afford the uniform
application of force which assures a high anchoring value.
The further embodiments of the expansion anchor assembly, shown in
detail in FIGS. 3 to 6, differ with regard to the assembly shown in
FIG. 1, only with regard to the expansion sleeve. Accordingly, only
the expansion sleeve is provided with new reference numerals.
In FIG. 3 the inside surface of the expansion sleeve 21 is seated
along its axial length within the cylindrical recess 3 in the
anchor bolt 1. A two-sided cross-sectional groove forms a reduced
thickness section 22 which is formed by means of dies with a
radially outwardly directed projection 23 extending for the full
circumferential width of the two-sided groove forming the reduced
thickness section 22.
In the embodiment in FIG. 4, a reduced thickness section 25
provides a weakened section in the expansion sleeve 24 defining a
saw-toothed like zone. The shaped configuration of the reduced
thickness section 25 is provided by forming dies. As a result,
radially outwardly from the reduced thickness section 25 there is a
projection 26 so that when expansion takes place a rupture of the
sleeve occurs along the reduced thickness section 25 in the wall of
the sleeve.
The embodiment in FIG. 5 is similar to the one shown in FIG. 4. In
this embodiment, an expansion sleeve 27 has a saw-tooth like
projection 28 produced by forming dies. The projection 28 is
connected by means of two cross-sectionally weakened sections 29 at
each end of the expansion sleeve 27. In FIG. 6 only one of the
weakened sections 29 is shown.
Preferably, each of the expansion sleeves illustrated in FIGS. 3 to
6 has, similar to the embodiment shown in FIG. 1 to 2a, two
diametrically oppostie projections. The comment on the function of
the sleeve provided above with regard to the embodiment of FIGS. 1
to 2a also apply with respect to the other embodiments.
While specific embodiments of the invention have been shown and
described in detail to illustrate the application of the inventive
principles, it will be understood that the invention may be
embodied otherwise without departing from such principles.
* * * * *